* layout.cc (Layout::find_or_add_kept_section): New function.

	* layout.cc (Layout::find_or_add_kept_section): New function.
	(Layout::add_comdat): Removed.
	* layout.h (struct Kept_section): Move out of class Layout.
	Remove trailing underscores from field names.  Add group_sections
	field.  Rename group_ field to is_group.  Change all uses.
	(class Layout): Declare find_or_add_kept_section, not add_comdat.
	* object.cc (Sized_relobj::Sized_relobj): Don't initialize
	comdat_groups_ field.
	(Sized_relobj::include_section_group): Use
	find_or_add_kept_section and Kept_section::group_sections.
	(Sized_relobj::include_linkonce_section): Likewise.
	* object.cc (class Sized_relobj): Don't define Comdat_group or
	Comdat_group_table.  Remove find_comdat_group and
	add_comdat_group.  Remove comdat_groups_ field.
	* plugin.cc (include_comdat_group): Use
	Layout::find_or_add_kept_section.